This invention relates to thin film optical devices and lasers and more particularly to an improved form of such devices and lasers in which controllable transverse modes are obtained using a two-dimensional distributed feedback periodic structure.
Reference is made to my article entitled "Proposal of Periodic Layered Waveguide Structures For Distributed Lasers", Journal of Applied Physics, Volume 44, Number 2, February 1973, pages 767-780 and to my previous patent applications entitled (a) Thin Film Lasers, Ser. No. 296,178 filed Oct. 10, 1972 and (b) Thin Film Optical Devices and Lasers, Ser. No. 331,675 filed Feb. 12, 1973, which disclose an invention relating to new classes of optical devices and lasers in which periodic variations are introduced in the structures of a thin film optical waveguide so as to create periodic reflections in the waveguide. These references are incorporated herein by reference. The periodic reflections thus generated give rise to distributed feedback (distributed coupling) between two counter running waves. In other words, the periodic variations in the waveguide structure of a distributed feedback laser serve a function similar to that of mirrors in conventional lasers. The previous invention, as disclosed in the article and referenced patent applications, generally provide for a periodic variation in a single or one dimensional arrangement in which the periodicity of the periodic variations used in the manufacture of such devices must be maintained with considerable accuracy. This limits the usefulness of the previously disclosed optical devices and lasers to materials having a relatively broad gain profile or otherwise requires the imposition of strict manufacturing tolerances with attendant high costs. There is a need, therefore, for a new and improved thin film devices and lasers. In addition, the previous invention provided an output beam in the form of a sheet of light which projects as a line on an intersecting plane. In many applications it is desirable to have a pencil beam of light which would project as a spot on an intersecting surface.